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Smooth pursuit (SP) was explored in dyslexics and non-dyslexics. Dyslexic children show similar gain of SP, and number and amplitude of catch-up saccades (CUS) as non-dyslexic children. The quality of binocular coordination is good for both groups; the only significant exception is for pursuit to the right for both smooth phase and CUS; dyslexics show higher disconjugacy. Decrement of binocular control during rightward pursuit only could reflect immaturity of oculomotor learning mechanisms needed to optimize binocular coordination for all directions. Yet, these observations need to be confirmed in a larger population including older children and compared with other populations, e.g. with right-to-left reading.

The origin of binocular coordination of saccades (central, peripheral) and the role of learning remain controversial (Hering vs Helmholtz). We will present evidence for learning: in young children (5 years) horizontal saccades are poorly yoked, coordination improves slowly with age particularly at near viewing distances. In dyslexic teenagers coordination of horizontal saccades is poor relative to non-dyslexics, suggesting slower learning. On the other hand, in healthy elderly participants (73 years) coordination of vertical saccades is intact, an example of a non ageing sub-system. To assess further central mechanisms, we applied TMS over the posterior parietal cortex of healthy adults, 100 ms after target onset. TMS impaired coordination particularly for rightward and downward saccades. Thus binocular coordination of saccades relies partially on cerebral function.experimental stages.

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